Biological systems, for example, are governed by a complex network of chemical reactions. These reactions include metabolic reactions that participate in the formation of compounds essential for the viability of cells and the destruction of waste and toxic compounds. Other reactions include chemical reactions that are involved in regulatory and signaling processes. For example, signals detected at the cell surface can initiate a cascade of chemical reactions that result in the transcription of certain genes. Biological systems are characterized by both the large number of distinct compounds and the reactions that inter-relate them.
Formal mathematical tools have been developed to model complex artificial networks, such as computer circuit design and architectures for fault-tolerant systems. Many of these tools use aspects of Boolean logic to provide robust representations of complex systems.